1. Field of the Invention
The present invention relates to a process for the preparation of polymers of .alpha.-olefins, especially homopolymers of ethylene and copolymers of ethylene and higher .alpha.-olefins, in which .alpha.-olefin monomer is polymerized in the presence of a four component coordination catalyst. In addition the present invention relates to a four component coordination catalyst for the polymerization of .alpha.-olefins.
2. Description of the Prior Art
Polymers of ethylene, for example, homopolymers of ethylene and copolymers of ethylene and higher .alpha.-olefins, are used in large volumes for a wide variety of end-uses, for example, in the form of film, fibers, moulded or thermoformed articles, pipe, coatings and the like.
Processes for the preparation of homopolymers of ethylene and of copolymers of ethylene and higher .alpha.-olefins are known. Such processes include processes in which the monomers are polymerized in the presence of a coordination catalyst, for example, a catalyst comprising a compound of a transition metal belonging to Groups IV-VIA of the Periodic Table and an organometallic compound of a metal belonging to Groups I-III of the Periodic Table.
A preferred process for the preparation of polymers and .alpha.-olefins is a so-called "solution" polymerization process, an example of which is described in Canadian Pat. No. 660,869 of A. W. Anderson, E. L. Fallwell and J. M. Bruce, which issued Apr. 9, 1963. A solution polymerization process is operated so that both monomer and polymer are maintained in solution in the reaction medium during polymerization of the monomer. In such a process relatively precise control of the degree of polymerization of the .alpha.-olefin monomer, and hence of the molecular weight of the polymer obtained, may be achieved by control of the reaction temperature. In an embodiment of a solution process, the molecular weight of the polymer may be further controlled by telomerization with hydrogen, as is described in Canadian Pat. No. 703,704 of C. T. Elston, which issued Feb. 9, 1965.
There are a number of advantages to a solution polymerization process, for example the ability to control the molecular weight of the polymer obtained, the ability to operate the process as a continuous process and to recover the polymer without the need for precipitation, the efficient use of catalyst and the properties of the polymer obtained.
A disadvantage of a solution polymerization process is that part of the catalyst remains in the polymer of ethylene. The catalyst remaining in the polymer, which may be referred to as "catalyst residue," may contribute to the colour of the polymer, to degradation of the polymer during subsequent processing of the polymer e.g. in extrusion, injection moulding and the like, and/or to degradation of the polymer on exposure of articles fabricated therefrom to ultra violet light. The amount of catalyst residue is related, at least in part, to the activity of the catalyst employed in the polymerization step of the process as the higher the activity of the catalyst the less catalyst that is, in general, required to effect polymerization at an acceptable rate. Catalysts of relatively high activity are therefore preferred in solution polymerization processes.
A solution polymerization process for the preparation of polymers of ethylene in which the catalyst is a coordination catalyst consisting of titanium tetrachloride, a vanadium compound and aluminum trialkyl is described in Canadian Pat. No. 635,823 of D. B. Ludlum, N. G. Merckling and L. H. Rombach, which issued Feb. 6, 1962. A polymerization process in which the catalyst is a coordination catalyst obtained by admixing (a) the hydrocarbon-insoluble solid reaction product of a hydrocarbon-soluble organoaluminum-magnesium complex and a titanium or vanadium compound containing halogen atom(s), and (b) an organoaluminum compound, is described in U.S. Pat. No. 4,004,071 of I. Aishima et al., which issued Jan. 18, 1977.
A solution polymerization process for the preparation of homopolymers of ethylene and copolymers of ethylene and higher .alpha.-olefins and a coordination catalyst for such a process have now been found. In the process, monomer is polymerized in the presence of the coordination catalyst which consists of a particular admixture of (a) a solution of an organoaluminum compound and an organomagnesium compound, with (b) a solution of a titanium compound and a vanadium compound.